Metric System of Measurement;
Interpretation of the International System
of Units for the United States

Interpretation of the
International System of Units
for the United States

This is a web version, including updated addresses, of the December
20, 1990 Federal Register notice.

This notice restates the interpretation of the SI for the United
States by the Department of Commerce. As provided by U.S. law,
the metric system of measurement to be used in the United States
is the SI as established by the General Conference on Weights
and Measures and interpreted or modified for the United States
by the Secretary of Commerce. The Secretary has delegated this
authority to the Director of the National Institute of Standards
and Technology.

Metric System of Measurement;
Interpretation of the International System of Units for the United
States

Agency: National Institute of Standards and Technology, Commerce.

ACTION: Notice.

SUMMARY: This notice restates the interpretation of the Department of
Commerce as to the International System of Units (``SI'') for
the United States. This interpretation was last published by the
Department of Commerce in the Federal Register on February 26, 1982 (47 FR 8399-8400). Although the contents
of the tables have not been changed in any significant way since
1982, in view of the amendment of the Metric Conversion Act of
1975 by the Omnibus Trade and Competitiveness Act of 1988, and
because over eight years have elapsed since the above Federal Register notice was published, it is deemed appropriate to once again
issue tables and associated text setting forth the interpretation
of the SI for the United States.

FOR FURTHER INFORMATION CONTACT: For information regarding the International System of Units,
Dr. Barry N. Taylor, Building 225, Room B161, National Institute of Standards and
Technology, Gaithersburg, Maryland 20899-0001, telephone number
(301) 975-4220. For more information regarding the Federal Government's
program for use of the International System of Units, Mr. James B. McCracken, Metric Program Office, Building 820, Room 306, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899-0001,
telephone number (301) 975-3686.

SUPPLEMENTARY INFORMATION: Section 5164 of Public Law 100-418, the Omnibus Trade and Competitiveness
Act of 1988, amends Public Law 94-168, the Metric Conversion Act
of 1975. In particular, section 3 of the latter act is amended
to read as follows:

``Sec. 3. It is therefore the declared policy of the United States
-

``(1) to designate the metric system of measurement as the preferred
system of weights and measures for United States trade and commerce:

``(2) to require that each Federal agency, by a date certain and
to the extent economically feasible by the end of the fiscal year
1992, use the metric system of measurement in its procurements,
grants, and other business related activities, except to the extent
that such use is impractical or is likely to cause significant
inefficiencies or loss of markets to United States firms, such
as when foreign competitors are producing competing products in
non-metric units;

``(3) to seek ways to increase understanding of the metric system
of measurement through educational information and guidance and
in Government publications; and

``(4) to permit the continued use of traditional systems of weights
and measures in nonbusiness activities.''

Section 403 of Public Law 93-380, the Education Amendments of
1974, states that it is the policy of the United States to encourage
educational agencies and institutions to prepare students to use
the metric system of measurement as part of the regular education
program. Under both this act and the Metric Conversion Act of
1975, the ``metric system of measurement'' is defined as the International
System of Units as established in 1960 by the General Conference
on Weights and Measures and interpreted or modified for the United
States by the Secretary of Commerce (sec. 4(4), Pub. L. 94-168;
sec. 403(a)(3), Pub. L. 93-380). The Secretary has delegated his
authority under these subsections to the Director of the National
Institute of Standards and Technology.

In implementation of this authority, tables and associated materials
were published in the Federal Register of February 26, 1982 (47 FR 8399-8400), setting forth the interpretation
and modification of the International System of Units (hereinafter
``SI'')for the United States.

Although the contents of the tables have not been changed in any
significant way since 1982, in view of the amendment of the Metric
Conversion Act of 1975 by the Omnibus Trade and Competitiveness
Act of 1988, and because over eight years have elapsed since the
above Federal Register notice was published, it is deemed appropriate
to once again issue tables and associated text setting forth the
interpretation of the SI for the United States.

The SI is constructed from seven base units for independent quantities
plus two supplementary derived dimensionless units for the dimensionless
derived quantities plane angle and solid angle, as listed in Tables 1a and 1b.

Units for all other quantities are derived from these nine units.
For example, in Table 2 are listed a number of SI derived units obtained from the base
units in a coherent manner, which means, in brief, that they are
expressed as products and quotients of the seven base units without
numerical factors.

Certain derived units that have been given special names and symbols
are listed in Table 3. They may themselves be used to express other derived units,
as is shown in Table 4. All the derived units given in Tables 3 and 4 have been obtained
from the base and supplementary units in the same coherent manner
indicated above.

The supplementary units of Table 1b may be used in the expression
of derived units as for the lumen in Table 3. Some additional
examples are given in Table 5.

Table 6 gives the 16 prefixes used to form multiples and submultiples
of the SI units. It is important to note that the kilogram is
the only SI unit with a prefix as part of its name and symbol.
Because double prefixes may not be used, in the case of mass the
prefixes of Table 6 are to be used with gram (symbol g) and not
with kilogram (symbol kg).

Certain units are not part of the SI, but are important and widely
used. The units in this category that are accepted for use in
the United States with the International System are listed in
Table 7.

In those fields where their usage is already well established,
the use of the units in Table 8 for a limited time is accepted, subject to future review.

As stated in the 1982 notice, metric units, symbols, and terms
that are not in accordance with the foregoing interpretation are
no longer accepted for continued use in the United States with
the International System of Units. Accordingly, the following
units and terms listed in the table of metric units in section 2
of the Act of July 28, 1866 that legalized the metric system of
weights and measures in the United States are no longer accepted
for use is the United States:

myriameter

stere

millier or tonneau

quintal

myriagram

kilo (for kilogram).

Although there is no formal comment period, public comments are
welcome on a continuing basis. Comments should be submitted to
Dr. Barry N. Taylor at the above address.

John W. Lyons,Director
[FR Doc. 90-21913 Filed 12-19-90; 8:45 am]

The following material is not part of the Federal Register notice.

Note 1: At the suggestion of its Consultative Committee for Units (CCU,
Comité Consultatif des Unités), the International Committee for
Weights and Measures (CIPM, Comité International des Poids et
Mesures) adopted four new SI prefixes at its September 1990 meeting.
These new prefixes were approved by the 19th General Conference
on Weights and Measures (CGPM, Conférence Générale des Poids et
Mesures) at its September-October 1991 meeting. Thus the new prefixes,
which are given in Note 1 Table, have become officially part of the SI and hence of Table 6.

Note 2: In 1980, the CIPM, which is under the authority of the CGPM,
interpreted the radian and steradian as so-called dimensionless
derived units for which the CGPM allows the freedom of using or
not using them in expressions for SI derived units. In 1995, the
CIPM, at the request of its CCU, asked the 20th CGPM to eliminate
formally the class of supplementary units as a separate class
in the SI. The 20th CGPM approved this request at its October
1995 meeting and thus the SI now consists of only two classes
of units: base units and derived units, with the radian and steradian
subsumed into the class of derived units of the SI. This means
that Table 1b is now officially part of Table 3. The option of
using the radian and steradian in expressions for other SI derived
units or not using them, as is convenient, remains unchanged.